1. Technical Field to which the Invention Belongs
The present invention relates to a transferring pressure roll and a transferring unit for use in the provision of a protective layer for covering an image (ink jet image) formed on a recording medium by an ink jet recording method and an ink jet recording apparatus comprising the transferring unit.
2. Related Art
An ink jet recording process is a printing process which comprises ejecting ink droplets from a minute jet nozzle of recording head onto a recording medium such as paper to which they are then fixed to form an image. In recent years, as a recording medium for ink jet recording there has been developed an ink jet recording paper comprising an ink-receiving layer mainly composed of a porous particulate material such as silica and alumina provided on a base such as paper and film. Such an ink jet recording paper can provide a high quality ink jet-recorded image comparable to silver salt system photograph. However, such an ink jet recording paper is inferior to silver salt system photograph in preservability (weathering resistance, gas resistance, friction resistance, etc.). The preservability of ink jet-recorded image has been considered important more and more with the expansion of application of ink jet recording technique to digital photographic service, commercial printing, etc. The provision of ink jet-recorded images which can be stored over an extended period of time is an important assignment of ink jet recording technique.
As a technique for enhancing the preservability or gloss of ink jet-recorded images there has been known a method which comprises laminating a transparent film or the like on a recorded material on the ink jet image surface thereof (ink jet-recorded image surface) to form a protective layer for covering the ink jet-recorded image. Examples of the film lamination method include a cold lamination method which comprises peeling a back paper (separator) off a normally adhesive film while laminating the adhesive film on the image surface, a heat (hot) lamination method which comprises laminating a thermoplastic resin film without back paper on the image surface while heating the thermoplastic resin film, and a heat transfer method which comprises subjecting a transferring film comprising a transparent film (transferable protective layer) provided on a heat-resistant substrate to heat transfer so that the transparent film is transferred to the image surface. Among these film lamination methods, the heat transfer method can form a thinner protective layer than the other lamination methods can. Thus, unlike the other lamination methods, the heat transfer method doesn't provide the image surface with excessive feeling of gloss. Accordingly, the heat transfer method has been noted as a lamination method which can enhance the preservability or gloss of image without impairing the inherent feeling or texture of recorded material. Examples of references of related art technique concerning the heat transfer method include JP-A-60-23096, JP-A-60-189486, and JP-A-61-230973.
Referring to the principle of the heat transfer method, a recorded material and a transferring film are normally laminated on each other in such an arrangement that the ink jet-recorded image surface and the transferable protective layer are opposed to each other to form a laminated sheet as shown in FIG. 6. The laminated sheet is then passed through the nip between a metallic heat pressure roll and a metallic receiving roll so that the transferable protective layer is fused and press-bonded to the ink jet-recorded image surface. The heat-resistant substrate is then peeled off the laminated sheet to obtain a desired recorded material with protective layer.
It is important in the aforementioned heat transfer method that there can be obtained a sufficient adhesion between the ink jet-recorded image surface and the transferable protective layer. However, this heat transfer method is disadvantageous in that if the ink jet-recorded image surface to which the transferable protective layer is transferred is a less smooth surface having a fine roughness (so-called finely roughened surface), the related art transferring unit can difficultly cause the molten transferable protective layer to enter in the indentation of roughened surface under heating and pressing, making it impossible to press-bond the transferable protective layer onto the ink jet-recorded image surface (finely roughened surface) with a good adhesion. As a result, bubbles enter in the gap between the ink jet-recorded image surface and the transferable protective layer. The heat transfer method is also disadvantageous in that when pressed by the aforementioned heat pressure roll, the raised portions on the finely roughened surface are crushed to level the roughness, impairing the inherent feeling or texture of recorded material.